Check their social media pages and look at their friends list. Notice how they interact with their friends or followers. You can usually tell by these interactions whether they actually know each other in person (faking a persona is possible; faking an entire group of friends isnt plausible).
Can online friends be dangerous?
Although meeting someone online could have a great outcome, it could also lead to very dangerous actions. The dangers of meeting someone over the internet can include sexual predators, thieves, blackmailers and the fear of not knowing who is actually behind the phone.
How do you know if an online friend is bad?
Some relatively sure signs of a toxic relationship include a persistent lack of balance between what is asked and what is given—attention, support, etc. An online friend who wants to co-opt your time through private chats, calls, “demands” for more attention, and so on, are often veering into toxic expectations.